”The mask is the meaning,” Roland Barthes wrote of Richard Avedon’s great portrait William Casby, Born in Slavery, Algiers, Louisiana, 1963—a face that bears witness to its society and history. In fact, though Avedon made his name revolutionizing fashion photography in postwar Paris, he remained fascinated all his life (he died in 2004) with politics, documenting everyone from the Weathermen to the Daughters of the American Revolution to a young senator from Illinois, Barack Obama. Timed to coincide with election season, the Corcoran Gallery of Art in Washington, D.C., is presenting “Richard Avedon: Portraits of Power” (through January 25;, an exhibition of some 200 photographs—including the portrait of Casby—that hold a mirror up to a half-century of American democracy.